1. Technical Field
This invention relates to compositions and methods for cleaning paint residues or deposits of paint commonly found in the interior walls of paint lines, tanks, and the like; and exterior surfaces such as the walls of paint booths, fixtures, and the like. More specifically, the present invention relates to a process and composition for cleaning interior and exterior surfaces of encrusted paint utilizing specific rheological agents or additives.
2. Discussion
Presently, the paint systems used in mass assembly operations such as the automotive and appliance industries generally rely on a central supply depot from which paint is passed through complex sets of paint lines to stationary paint stations located within an enclosed paint booth. The parts are painted as they pass through paint booths on a moving conveyor. Because the system uses several tanks, valves, pumps, bypass lines and the like, a variety of paints can be delivered to a given paint station over common lines. Such a system, however, requires constant maintenance and housekeeping in order to maintain an efficient operation. Without this maintenance, the central supply depot becomes coated and contaminated with a variety of paints, the paint lines become clogged with encrustation of paint, the paint stations and spray nozzles become inoperative and the paint booths become contaminated from overspray during the paint cycle.
One approach to cleaning paint systems, and in particular the paint delivery lines used within the paint system, recycles a variety of solvents and solvent additives to clean the system. The solvents used may be organic or aqueous-based, although organic-based solvents are generally preferred for most present day systems. The solvent additives used may include detergents, surfactants, sand, mica or even other solvents, in the case of organic-based solvents; or alkaline or acidic additives in the case of aqueous-based solvents.
A more recent approach is to use inert particulate organic polymeric materials dispersed in an organic solvent as disclosed in U.S. Pat. No. 4,968,447, to Dixon, et al. This system and other similar systems rely on the abrasive action of the particulates to loosen encrusted deposits from the paint lines during the cleaning cycle. However, such use of inert particulate organic polymeric materials has several disadvantages. Build-up occurs in the restricted areas of paint lines such as valves, drop lines, bypass lines, etc. which, once formed is difficult to break up and remove. This difficulty in removing all traces of the particulates necessitates the use of a greater number of rinse cycles, and sometimes the use of a paint compatible resin rinse, followed by a paint compatible solvent rinse, in order to ensure removal of all the particulates.
In practice, it is difficult to remove all of these particulates in some restricted areas and therefore the system must be dismantled in order to dislodge the obstruction. Also, although sophisticated filtration systems are used in these paint systems, even the slightest flaw in the filtering system will cause paint defects if any of these inert organic particulates are not retained within the filters.
Another disadvantage of inert organic particulate materials is their tendency to build up on the external walls of vessels and fixtures. This results from the evaporation of the organic cleaning solvents depositing the inert organic polymeric particulates as a powdery mass on the surface. This increases the housekeeping problem since any powdered substance easily becomes airborne or is transferred by clinging to workers' shoes or clothing. In some cases, where the cleaning solvent is not sufficient to remove all of the paint residue, the paint residue becomes even more encrusted due to the additional inert organic particulates when the cleaning solvent is allowed to evaporate. Obviously, cleaning solvents using these types of inert organic polymeric particulates are a housekeeping problem and a potential source of contamination to the paint system.